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CASE REPORT

A Symptomatic Anomalous Variant Of The Medial Meniscus.  A Case Report And Review Of The Literature.

Saket Tibrewal*, Sunil Garg#, Sheo B Tibrewal**

* Dept. of Trauma & Orthopaedic Surgery, Guy’s & St. Thomas’ Hospitals,     London
#Dept. of Trauma & Orthopaedic Surgery, King’s College Hospital, London
**Dept. of Trauma & Orthopaedic Surgery, Queen Elizabeth Hospital, London 

Address for Correspondence:
Mr Saket Tibrewal 
‘Rosewood’
, 59 Elmstead Lane
Chislehurst
, Kent  BR7 5EQ
Email: sak11@hotmail.com
Tel: 07931 767811
Fax: 020 8402 4849

J.Orthopaedics 2007;4(2)e28

Introduction:

Congenital anatomical variations of the medial meniscus have been very rarely reported in the literature.  We present a unique case of an abnormal shape and attachment of the anterior horn of the medial meniscus not previously described in the English literature.

Case Report:

A 15 year old boy presented with persistent pain in his right knee which he related to an accident which had occurred 6 years previously.  The general practitioner’s letter stated that “the knee locks at times and he has difficulty in running and with playing games”.  On presentation he complained of pain on both medial and lateral aspects of the right knee with a history of locking.  He also complained of difficulty in running and playing any sports. 

On clinical examination the quadriceps muscle was noted to be slightly wasted.  There was no patello-femoral discomfort.  The knee had full extension but flexion beyond 125 degrees was painful.  There was marked tenderness over both medial and lateral menisci.  McMurray’s test was positive for the medial meniscus.  Lachmann’s test was negative.  Radiographs did not reveal any significant abnormality.  In view of his symptoms his name was placed on the waiting list for arthroscopy of his right knee. 

At arthroscopy, the patello-femoral joint was found to be normal.  The anterior horn of the medial meniscus was found to be abnormal in its shape, size (i.e. it was hypoplastic), location and insertion (fig. 1,2,3).  The size of the anterior horn of the medial meniscus was smaller in comparison to the rest of the medial meniscus and the attachment of the anterior horn was not complete over the non-articular anteromedial surface of the tibia (fig. 1, 2, 3).  The anterior half of the medial meniscus was seen to slope in its entirety towards the anteromedial aspect of the tibia below the margins of the articular surface with its insertion just below this (fig. 1, 2, 3).  As a result in extension the medial femoral condyle was resting directly on the articular surface of the medial compartment of the tibia rather than the anterior horn of the medial meniscus as is normally the case.  However, the meniscus was intact and no meniscal tear was found on probe examination.  There was a localised impingement synovitis around the anterior part of the medial meniscus and this was debrided.  The lateral compartment was found to contain grade 1 to 2 degenerative changes in a localised small area over the lateral tibial plateau.  There was minor fraying of the lateral meniscal cartilage and this area was trimmed to stable margins. 

Post-operatively the patient became asymptomatic and the portal wounds healed well.  He was referred for out-patient physiotherapy and at the time of reporting he remains asymptomatic. 

Fig 1

Fig 2

Fig 3

Embryology of the medial meniscus  

During embryological development the menisci and cruciate ligaments appear at approximately seven weeks.  These structures are formed directly from the blastema and not from the secondary invasion of the synovial tissue into the joint.  It is reported that the menisci and cruciate ligaments first appear when the crown-rump length is approximately 22 to 23 mm; even at this early stage of development there is an even transition between the tissues forming the menisci and that forming the cruciate ligaments.  An anatomical study by Clarke & Ogden demonstrated that anterior extensions from both menisci to anterior cruciate ligaments can be present after birth1.

Discussion :

In the normal adult knee, the anterior convex margin of the anterior horn of the lateral meniscus is attached to the anterior end of the medial meniscus by means of the transverse meniscal ligament. At times, this ligament is absent. In adults, the anterior horn of the lateral meniscus inserts on the tibia in front of the tibial spine and its insertion is partly blended with the anterior cruciate ligament. The anterior horn of the medial meniscus inserts on the tibia anterior to the insertion of the anterior cruciate ligament; it remains distinct from the anterior cruciate ligament. 

Only a few reports of anomalous insertion of the medial meniscus exist, and they include abnormal insertion of the medial meniscus into the anterior cruciate ligament2, anomalous insertion of the anterior horn of the medial meniscus into the intercondylar notch of the femur with an absent transverse meniscal ligament3 , and a case of an anomalous band in continuity with the medial meniscus that extended from the posterior horn area of the medial meniscus to insert into the midportion of the anterior cruciate ligament4 .  Other anomalies (variants) of the medial meniscus described in the literature include discoid variants, discoid variants associated with a cyst, discoid medial meniscus bilaterally, absent fixation of the transverse meniscal ligament to the tibial plateau, buckled meniscus, hypoplasia of the anterior horn, the posterior horn, the entire meniscus, the ACL, and anomalous attachment of the posterior horn. 

 In a morphologic study of 48 cadaveric knees, Berlet et al reported four tibial insertion locations of the medial meniscus5:  Type I insertions were located in the flat intercondylar region of the tibial plateau; type II occurred on the downward slope from the medial articular plateau to the intercondylar region; type III occurred on the anterior slope of the tibial plateau; and in type IV there was no firm bony insertion of the anterior horn of the medial meniscus. The occurrence for type I was reported to be  59%; type II, 24% ; type III, 15%; and type IV, 3% . 

In an arthroscopic study of variants of the anterior horn of the medical meniscus the authors classified medial meniscus insertion into the following four categories6 - the ACL (anterior cruciate ligament) type, where the anterior horn of the medial meniscus was attached to the ACL; the transverse ligament type, where the anterior horn of the medial meniscus was attached to the transverse ligament; the coronary ligament type, where the anterior horn of the medial meniscus was attached to the coronary ligament; and the infrapatellar fold type, where the anterior horn of the medial meniscus was attached to the infrapatellar synovial fold.   

We report an abnormal insertion of a hypoplastic anterior horn of the medial meniscus onto the margins of the anterior part of the tibial plateau.  It is well known that with the knee in extension the medial femoral condyle rests on the anterior horn of the medial meniscus as can be seen from the MRI scan(fig. 4 ).  In a case such as ours where there is no medial meniscus covering the articular surface of the anterior portion of the medial tibial plateau, in an extended knee the articular cartilage of the medial femoral condyle rests directly on the articular cartilage of the tibial plateau anteriorly thus placing these portions of the articular cartilage at risk for early degenerative changes.  In our case there was impingement synovitis in the abnormal area of the medial meniscus and debridement of this synovitis was helpful in relieving these symptoms.   

Fig 4

Variation in the insertion patterns of the meniscus may have other clinical implications as some of the atypical insertions may be unable to resist peripheral extrusion of the loaded meniscus, placing it at risk for anterior subluxation and causing atypical anterior knee pain.  Awareness of variance in insertion patterns and congenital anomalies may also be valuable in medial meniscal harvest and transplantation. 

Reference : 

  1. Clark, C. R., and Ogden, J. A.: Development of the menisci of the human knee joint. Morphological changes and their potential role in childhood meniscal injury. J. Bone and Joint Surg., 65-A:538-547, April 1983.

  2. Santi MD, Richardson AB.  Bilaterally painful anomalous insertion of the medial meniscus in a volleyball player with Marfanoid features.  Arthroscopy. 1993;9(2):217-9.

  3. Shea KG, Westin C, West J.  Anomalous insertion of the medial meniscus of the knee. A case report.  J Bone Joint Surg Am. 1995 Dec;77(12):1894-6.

  4. Bhargava A, Ferrari DA.  Posterior medial meniscus-femoral insertion into the anterior cruciate ligament. A case report.  Clin Orthop Relat Res. 1998 Mar;(348):176-9.

  5. Atay OA, Doral MN, Aydingoz U, Leblebicioglu G. Bilateral discoid medial menisci: association with bone changes in the tibia.  Knee Surg Sports Traumatol Arthrosc. 2001 Jul;9(4):217-20.

  6. Pinar H, Akseki D, Karaoglan O, Ozkan M, Uluc E. Bilateral discoid medial menisci.  Arthroscopy. 2000 Jan-Feb;16(1):96-101.

  7. Kim SJ, Lee YT, Kim DW. Intraarticular anatomic variants associated with discoid meniscus in Koreans.  Clin Orthop Relat Res. 1998 Nov;(356):202-7.

  8. Arjun S, Takahashi S, Tang Y, Nakane N, Yonemitsu H. MR appearance of anomalous insertion of the medial meniscus. A case report.  Acta Radiol. 1998 Sep;39(5):554-6.

  9. Akgun I, Heybeli N, Bagatur E, Karadeniz N.  Bilateral discoid medial menisci: an adult patient with symmetrical radial tears in both knees.  Arthroscopy. 1998 Jul-Aug;14(5):512-7. Review.

  10. Kim SJ, Choi CH.  Bilateral complete discoid medial menisci combined with anomalous insertion and cyst formation. Arthroscopy. 1996 Feb;12(1):112-5.

  11. Kim SJ, Kim DW, Min BH.  Discoid lateral meniscus associated with anomalous insertion of the medial meniscus.  Clin Orthop Relat Res. 1995 Jun;(315):234-7.

  12. Volkov MV, Samoilovich EF, Serafin IuIa.  Congenital and acquired deformities of knee joint menisci in children.  Khirurgiia (Mosk). 1994 Aug;(8):38-45. Russian.

  13. Schonholtz GJ, Koenig TM, Prince A. Bilateral discoid medial menisci: a case report and literature review.  Arthroscopy. 1993;9(3):315-7. Review.

  14. Samoilovich EF, Serafin IuIa.  Development anomalies of the menisci and transverse ligament of the knee.  Ortop Travmatol Protez. 1991 Nov;(11):25-30. Russian.

  15. Berlet GC, Fowler PJ.  The anterior horn of the medical meniscus. An anatomic study of its insertion.  Am J Sports Med. 1998 Jul-Aug;26(4):540-3.

  16. Ohkoshi Y, Takeuchi T, Inoue C, Hashimoto T, Shigenobu K, Yamane S.  Arthroscopic studies of variants of the anterior horn of the medical meniscus.  Arthroscopy. 1997 Dec;13(6):725-30.

This is a peer reviewed paper 

Please cite as :Saket Tibrewal : A Symptomatic Anomalous Variant Of The Medial Meniscus.  A Case Report And Review Of The Literature.

J.Orthopaedics 2007;4(2)e28

URL: http://www.jortho.org/2007/4/2/e28

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